The sounding of the hour by a variable number of strikes, and possibly also of the half-hour by a single strike, is conventionally accomplished with the aid of a trigger actuated by the minute shaft of the clockwork. The number of strikes is determined by a mechanical counter which usually comprises a toothed segment or rack displaced by an hour cam before each striking operation, the cam being driven by the hour shaft of the clockwork and having a generally spiral ramp surface composed of discrete dwells of different radii which advance the cam to a different extent from its home position. A solenoid-operated pawl retracts the rack, one tooth at a time, during the execution of the strikes; when the rack returns to its home position, the operation is stopped. Before the half-hour, the rack is advanced by just one tooth regardless of the position of the hour cam.
Such an electrically operated striking mechanism, originally intended mainly for tower clocks, has a large number of movable parts and is too bulky for use in more compact timepieces; it is also subject to malfunctions due to wear.